Metal oxide-hydrogen batteries, such as nickel oxide-hydrogen batteries have seen use as aircraft starter batteries and in aerospace applications because they are rechargeable, have extremely long cycle life and provide a uniform output during the entire discharge cycle.
In the typical nickel oxide-hydrogen battery, the battery cells are sealed in an outer pressure vessel that contains pressurized hydrogen gas. On discharge of the battery, the hydrogen gas diffuses through the electrolyte surrounding the catalyst surfaces of the negative plates and becomes disassociated to the mono-atomic form. The mono-atomic hydrogen is ionized and combines with hydroxyl ions to form water with an electron being released in the process of forming each hydrogen ion. In addition, hydroxyl ions are formed at the positive electrode by the reaction of water with the available oxygen content of the nickel oxide. As a result of these reactions an electron current is produced in the exterior circuit.
On recharging, the reaction is reversed, with the recharging being characterized by the regeneration of hydrogen at the negative electrode and the reoxidation of the nickel hydroxide at the positive electrode.
A nickel oxygen-hydrogen battery that contains a plurality or series of cell modules is commonly referred to as a common pressure vessel (CPV). In a CPV the individual cell modules are in the form of a side-by-side stack and as disclosed in U.S. Pat. No. 4,957,830 two stacks of semi-cylindrical cell modules are contained within the cylindrical pressure vessel. Alternately, the cell modules can be cylindrical or rectangular in configuration.
As described in the aforementioned patent, heat transfer plates or fins can be located between each pair of adjacent cell modules and act to transfer heat from the cell modules to the outer pressure vessel.
In the past the metal heat transfer fins have been integral with a semi-cylindrical shell, the fins being located between adjacent cell modules while the semi-cylindrical shell is in disposed in engagement with the inner surface of the pressure vessel. This type of heat transfer member has been traditionally formed by machining the shell and fins from a solid block of metal, or alternately individual fins have been brazed to the inner surface of the metal shell. In either case, the production of the heat transfe member has been extremely expensive and time consuming.
It is also important for effective heat transfer that the cell modules be in intimate contact with the flat heat transfer fins. With the machined or brazed construction as used in the past, the spacing between fins was fixed and the spacing was established to accommodate maximum tolerance of cell module thickness. Because of this, certain cell modules in the stack would not be in snug intimate contact with the fins which detracted from heat transfer to the outer pressure vessel.
As a result of expansion of the pressure vessel diameter due to internal pressure increases, a gap can occur between the heat transfer members, as used in the past, and the vessel wall. Such a gap could allow the stack of cell modules to collide with the vessel wall when the vessel is subjected to vibration or impact and possibly cause damage to either the cell modules or the vessel wall.